It is known that energy equals force times distance. In head impact, the impact forces and impact energy translate into accelerations, both linear and rotational, that are experienced by the brain and brain stem during a hit. In an attempt to minimize these impact forces, energy absorbers are deployed between a rigid surfaces and for example a synthetic turf systems, to reduce the forces experienced by the brain and body to minimize the risk of serious injury due to contact with the turf system. While the percentage of concussions that occur due to contact with the turf vary from sport to sport, the accepted range is somewhere between 7% and 25%. While reducing the frequency of concussions due to impacts with the turf system is desired, these systems need to be deployed and function in a manner that does not increase the frequency and severity of injuries. Ideally, the turf system should perform such that it balances impact energy management and playability.
The popularity of synthetic turf systems continues to grow. The majority of new systems have fabric backed needle punched polymer fibers with an infill system that typically includes sand for ballast and elastomeric rubbers for impact energy management. Well maintained systems perform acceptably when tested with low energy flat missile tests. These flat missiles were originally developed to measure soil compaction for construction, not intended as a measure of head impact severity.
The head impact criteria (HIC) output from flat missiles measure acceleration along only one axis. They do not address non-linear events and lack bio-fidelity. These turf systems, when tested using a hemispherical head form that more closely approximates a human skull, can easily produce HIC values in excess of 1000 corresponding to a 90% probability of moderate head injury. There is clearly a need and an opportunity to improve these systems.
In recent years a secondary layer has been interposed between the turf/infill system and the compacted base. This layer is referred commonly referred to as a “shockpad” and has been historically manufactured from foam or rubber. While foam and rubber shock pads do provide some additional stroke to the system, they have proven to be relatively inefficient in their ability to absorb energy. Further such systems have various problems relative to draining and floating when exposed to a heavy rain.
The effectiveness of any energy absorbing system depends on its relative stiffness and crush efficiency over the range of impact energies the system is expected to experience. An ideal energy absorbing system would be capable of increasing or decreasing its ability to absorb energy as the speed and subsequent impact energy increases or decreases respectively. Additionally, the ideal force displacement response for linear impacts would have a relatively “square wave” shape. Idealized square wave energy absorbers ramp up quickly and maintain a relatively constant load throughout the impact event that maximizes the amount of energy capable of being absorbed. Foams and rubber absorbers ramp up slowly, lack a square wave plateau, and bottom out at less than 65% stroke.
Shockpads serve other functions in addition to absorbing energy. They need to be easy to install and, once installed, should be able to withstand the expansion and contraction that occurs as temperatures rise and fall without creating a noticeable bulge or seam on or underneath the turf surface. Shockpads also need to manage irrigation and precipitation that drains onto them through the turf/infill system. Both vertical and horizontal water management needs to be considered. Turf systems that do not drain well can create serious issues for the turf surface. The system also needs to be resilient, given that several thousand impacts could be received by the turf throughout its life cycle. Further, many foams float or have difficulty draining when exposed to heavy rain. Additionally, their long term durability and resiliency when exposed to abrasions and repeat impacts can be an issue.
The interface between the shockpad and the underside of the turf also bears consideration. High levels of slip or friction between the two has the potential of affecting the playability and safety of the turf system. Protuberances which promote some level of “bite” to the underside of the turf is to be considered. Finally, the shockpads are in a moist environment over long periods of time. Shockpad materials may be prone to hydrolysis and degrade in the presence of water and chemicals that migrate through the turf system into the underlying shockpad.
In an effort to improve the consistency of the turf systems, several shockpad systems have been developed and deployed in recent years. The three main categories of these systems include pour in-place products, rolled goods, and panels.
Pour-in-place systems are applied in a manner similar to cement or asphalt. Ground crumb rubber is combined with a thermosetting binder and then manipulated using conventional paving equipment. Once cured, these systems compliment the performance of the turf system. Historically, these systems have been prone to variation based on the installed thickness and chemical mixing of the binder and rubber. They are also more prone to breakdown due to several factors.
Rolled goods are one of the easiest materials to install. Large rolls of foam are unrolled and then either taped or stitched together to create a uniform surface. Rolls are produced from a variety of materials including ground post consumer polyurethane foam, SBR rubber, cross-linked olefin foams, and expanded polypropylene foam. These materials typically tend to have issues under the turf at the seams between rolls and can promote buckling of the turf during expansion and contraction.
Foam panels, typically made from low density EPP foam with or without formed interlocking sections have also been used. These systems react well to expansion and contraction. However their light weight and low density proves challenging during both installation when they have a tendency to “sail” in the wind, and also during heavy rainfall where the shockpads float until the water dissipates. Further a low packing density results in high transportation costs.
Floors, walls and ceilings are often subject to percussive impact. This is particularly true in sports settings in which the field and boundary wall surfaces are the recipients of impacts from players. Similarly, in military and industrial settings, blast and work mats are utilized to absorb impact forces that result from explosive events, crashes, falls and the like. These mats function to at least partially absorb these impact forces, thus cushioning the force imparted to the individual. Floorboards also receive undesirable impacts from people (or equipment) falling from an elevated distance, not only in construction areas but also in homes.
Flooring and wall structures, for example, have evolved over the years to include technology that absorbs energy transmitted during impact. For instance, synthetic and artificial turfs have been introduced into such impact-receiving surfaces as football and baseball fields in which rubber pebbles help to absorb an impact force applied thereon, reducing the risk of injury for the participants.
In recent years, excessive bodily injuries and concussions have gained more attention as diagnostic tools and methods have also evolved. Athletes and workers involved in an impact with floors or walls are susceptible to serious injury as a result of such impact. There is a desire for floors and walls in these settings to be equipped to absorb the impacting force and thereby provide better impact protection to the individuals or objects that may impact the floor and wall surfaces.
Among the references considered before filing this application are these: U.S. Pat. Nos. 8,221,856; 8,226,491; 8,568,840; U.S. patent publication Nos. 2014/0311074; 2014/0311075; EP 2154291; and WO 2013/183989A1.